How much powdered ginger do you use in place of 2 teaspoon grated fresh ginger?

When all else fails, go to "Joy of Cooking" --see "equivalents and or substitutions, and I quote:

1 Tsp raw ginger = 1/8 tsp pwd. This info is usually on the spice container, but I

use a less expensive brand and it does not have the info. cmg